Typically, a cement retainer is used in an oil or gas well at the upper limit of a section of the well casing which is to be treated with cement for closing leaks or perforations. In preparing a well for cementing, an assembly comprising a mechanical setting tool and a cement retainer is lowered with the tubing string into the well to a position located immediately above the section of the well to be cemented. Desirably, as the assembly is lowered, a cement valve in the retainer is held open to the passage of well fluids so as to ease lowering of the assembly into the well. Once located in the desired position, the tubing string carrying the assembly is manipulated to cause the slip set carried by the retainer to deploy and anchor the retainer within the casing. At the same time that the slips are set, sealing elements in the retainer are compressed axially to expand radially outward and thereby seal between the tubing string and the casing. This keeps cement from flowing upwardly in the annulus between the tubing string and the interior of the casing when the cement is forced under pressure from the bottom of the retainer into the well section. To make sure that cement does not leak from the tubing string or across the packing elements during cementing, both the tubing string and the annulus are usually pressure tested separately before cementing..
The usual procedure for cementing also requires that the setting tool be disconnected from the retainer to spot the cement in the well with the valve closed. Cement spotting involves pumping of a quantity cement through the tubing and discharging the volume of well fluid displaced by the cement from the annulus at the top of the well. Once the cement reaches the lower end of the tubing string, as determined by the volume of well fluid displaced from the annulus, the tubing string is reconnected to the retainer and the valve is opened. This procedure avoids forcing excess fluid into the formation where the leaks or perforations are located. After a measured quantity of cement is injected into the well, it is desirable to quickly disconnect the setting tool from the retainer and coincidently therewith close the valve. Quick disconnection avoids cementing the setting tool in the retainer and the closing of the valve is important to keep cement from being forced back through the valve by pressure in the well beneath the retainer.
Different examples of prior cement retainers are disclosed in U.S. Pat. Nos. 3,387,659, 3,448,806 and 3,465,821. The cement retainer and setting tool assembly shown in U.S. Pat. No. 3,465,821 includes a set of upper slips confined in a running-in position by a slip retainer sleeve whose lower end portion is telescoped over an upper end portion of the slips. A drag mechanism above the sleeve includes a threaded connection with a control sleeve which in turn, is releasably latched with an operating mandrel connected to the tubing string carrying the assembly so that, once the assembly is positioned properly in the well, rotation of the tubing string causes the sleeve to move upwardly on the control sleeve freeing the slips to be set against the interior wall of the well casing. At the same time, the latch between the control sleeve and the mandrel is released and, thereafter, an upward pull on the tubing string lifts the cement retainer with the upper slips abutting the lower end of the control sleeve so as to be wedged outwardly and anchored against the interior wall of the casing.
A releasable connection provided by abutment between coupling lugs on a tubular extension of the operating mandrel and shoulders on another mandrel in the retainer disclosed in patent 3,465,821 serves to transmit upward force from the tubing string to the retainer for setting the slips. The lugs and shoulders are spaced angularly around the respective members to which they are attached and index pins on the retainer mandrel riding within slots in the operating mandrel extension cause the mandrel to rotate between indexed positions as the tubing string is alternately raised and lowered. In this manner, the lugs are positioned relative to the shoulders so they either engage or avoid engagement with each other as the tubing string is lifted. When the lugs and shoulders are positioned to avoid engagement with each other, the setting tool may be disconnected from the retainer by lifting on the tubing string. Rotation of the tubing string by indexing of the pins in the slots also opens and closes a valve in the retainer. The indexing is such that the valve remains closed when the lugs and shoulders are positioned to avoid engagement.
In service use of foregoing arrangement, after testing or spotting cement and reconnecting the setting tool with the cement retainer to squeeze cement through the retainer, it is necessary to manipulate the tubing string up, down and back up again before the setting tool will disconnect from the cement retainer. The first upward movement of the tubing string is for closing the valve and the following downward and upward actions are to index the relative positions of the lugs and shoulders so they avoid engaging each other when the tubing string and setting tool are pulled from the well.
U.S. Pat. No. 3,448,806 discloses a cement retainer and setting tool assembly which is similar to the one disclosed in U.S. Pat No. 3,465,821, at least with respect to the arrangement for setting the slips. In the arrangement disclosed in U.S. Pat. No. 3,448,806, however, the valve at the lower end of the retainer is opened and closed by vertical movement of a mandrel extension which releasably connects with a vertically movable valve sleeve. In a lower position of the sleeve, the valve is opened, and in an upper position, the valve is closed. Latch fingers provide the connection between the mandrel extension and the valve sleeve for pushing the sleeve into its lower open position such as when the valve is opened after pressure testing. The fingers release from the mandrel when it is raised and a coil spring urges against the underside of the valve sleeve to push it upwardly into its closed position when the fingers are released. In order to change the position of the valve sleeve from the position it is in when the retainer is being lowered into the well, it is necessary first to set the slips on the cement retainer and then rotate the tubing string. This rotation both shears a pin and causes a ratchet nut to move upwardly from a locked position connecting the setting tool with the retainer mandrel into a release position within which the tubing string may be moved vertically to either open or close the valve as desired.
The cement retainer and setting tool assembly disclosed in the aforementioned U.S. Pat. No. 3,387,659 is functionally similar to the assemblies described above. In the assembly disclosed in patent 3,387,659, however, slips carried by the retainer are set initially against the interior wall of a well casing by the force stored in a coil spring which acts through a drag mechanism to urge a setting sleeve downwardly against the slips. While the assembly is being run in the well on the lower end of a tubing string the spring is held compressed between a tension nut and a hydraulic piston. The latter is supported upwardly against the lower end of the spring by hydraulic fluid captivated in a chamber below the piston. Rotation of the tubing string carrying the assembly releases the fluid, allowing the spring to shift the drag mechanism downwardly against the setting sleeve. The latter, in turn, is pushed by the mechanism to initially set the slips. Thereafter, an upward pull on the tubing string causes the slips to set further, packing off the retainer in the well. The upward force for anchoring the slips securely in the casing is transmitted from an operating mandrel of the setting tool, to a separate mandrel in the cement retainer through a connection which includes a frangible pin, a pair of spring biased latching dogs and abutting shoulders. The latching dogs and abutting shoulders are connected to the operating mandrel and the retainer mandrel, respectively. When running the assembly into the well casing with the retainer valve held open, the frangible pin serves to support the shoulers in a spaced relationship but in setting the slips, lifting on the tubing string fractures the pin and the operating mandrel and the retainer mandrel slide relative to each other until the shoulders contact each other. As the mandrels slide, an actuator connected to the valve is lifted thereby closing the valve. Once the pin is broken, instead of upward setting force being transmitted through the pin and the latching dogs, the force is transmitted through the abutting shoulders and the latching dogs. In order to release the latching dogs for separating the setting tool from the cement retainer, the tubing string is slacked-off (lowered) so the latching dogs engage with a release sleeve carried on the retainer mandrel. Once engaged with the release sleeve, the latching dogs are positioned to be pulled upwardly with the operating mandrel when the setting tool is removed from the retainer.